Circuit arrangement for controlling a gas discharge tube



y 30, 1967 P. H. G. VAN VLODROP 3,323,011

CIRCUIT ARRANGEMENT FOR CONTROLLING A GAS DISCHARGE TUB E Filed Aug. e, 1965 FIG.1 W

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INVENTOR.

PETER H.G VAN VLODROP United States Patent 3,323,011 CIRCUIT ARRANGEMENT FOR CONTROLLING A GAS DISCHARGE TUBE Peter Hubertus Gerardus van Vlodrop, Emmasingel, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Aug. 6, 1963, Ser. No. 300,310 Claims priority, application Netherlands, Aug. 27, 1962, 282,548 11 Claims. (Cl. 315-166) The invention relates to a circuit arrangement for controlling a gas or vapour filled discharge tube having a" control-electrode. More particularly, the invention relates to a circuit for controlling the angle of ignition of an electric discharge tube by means of positive voltage pulses having a progressively rising leading edge which are applied to said electrode. The pulses are superimposed on the voltage of a bias voltage source, which has its .positive terminal of which is connected to the cathode of the discharge tube.

Such arrangements are described in United States Patents 2,956,207 and 3,041,500, in which the positive pulses are derived from an alternating voltage, for example, the A.C. supply voltage, so that the ignition of the gas discharge tube can readily be synchronised with said alternating voltage. At the same time the phase of the ignition relative to said alternating voltage can readily be controlled within a range of nearly 270 electrical degrees by varying the voltage of the bias voltage source and/or by shifting the phase of the positive voltage pulses with respect to the alternating voltage.

In order to fully utilize this very wide control-range, it is in many cases necessary to take measures to insure the rapid extinction of the discharge tube subsequent to its ignition. Often, particularly when the anode of the gas discharge tube is supplied with a direct supply voltage, this extinction is prevented by the fact that the progressively rising leading edge of the control-voltage pulse extends after the instant of ignition, during a time varying with the ignition phase and which may, at the most, be nearly 270 of one period of the alternating voltage.

The invention provides a solution of the problem caused by said extension of the control-voltage pulses. The circuit arrangement according to the invention is characterized in that the circuit of the control-electrode of the discharge tube includes a resistor connected in series with the main current path of an auxiliary discharge tube, one of the main current path electrodes of which is connected to the negative terminal of the bias voltage source. The positive voltage pulses are applied across the main current path of said auxiliary discharge tube in. a manner such that the auxiliary discharge tube ignites after the first-mentioned discharge tube. As a result, the negative voltage of the bias voltage source is applied to the controlelectrode of the first discharge tube via the auxiliary dis charge tube and the resistor after each ignition of the first discharge tube and extinguishes the discharge between its cathode and control electrode.

It should be noted here that it is known per se from Swiss patent specification 176,745 to produce a rapid deionisation of a gas discharged tube subsequent to its ignition by connecting the control-electrode of this tube, subsequent to ignition to the cathode thereof or to a source of negative bias voltage having a low internal resistance, by means of a low impendance, for example, an auxiliary discharge tube. Moreover, the British patent specification 487,466 describes a circuit arrangement for controlling a gas discharge tube in which the termination of a conductive period is brought about by the ignition of an auxiliary gas discharge tube by means of which a 3,323,011 Patented May 30, 1967 "ice blocking negative bias voltage is fed to the controlelectrode of the main discharge tube.

However, in the circuit arrangement according to the invention, the control-electrode of the main discharge tube is biased negatively by the bias voltage source immediately :after the ignition of this tube. At the same time, the sustained ascending portion of the progressively rising leading edge of the control-voltage pulse is suppressed and any ion flow passing through the circuit of said controlelectrode is limited by a resistor connected in series with the main current circuit of the auxiliary discharge tube.

If the component parts of the anode circuit of the main tube are correctly chosen, the extinction of the main discharge tube is obtained reliably within a wide controlrange of, for example, 240 or more, even if the anode of said tube is supplied with direct voltage since it is impossible for this tube to remain statically conducting.

With the circuit arrangement according to the invention, strong, wide pulses can readily be produced in the anode of a main discharge tube the anode of which is fed with a direct-voltage, and said pulses having a constant width and amplitude throughout the control-range.

The invention will be described with reference to the drawing.

FIG. 1 shows the circuit diagram of one embodiment of the circuit arrangement according to the invention and FIG. 2 shows time diagrams of the voltage at difierent points of said circuit arrangement.

The circuit arrangement shown in FIG. 1 comprises a gas discharge tube 1, for example, a thyratron having a cathode, an anode, and a control or ignition electrode which is to be controlled by means of positive voltage pulses.

In order to provide a means for readily varying the instant of ignition of the tube 1, for example, the phase of said instant, with respect to an alternating voltage, voltage pulses having a slightly sloping leading edge, for example, sawtooth pulses, are employed. The instant of ignition is controlled by the variation of a bias voltage on which said pulses are superimposed. As is shown, an alternating voltage V having a peak value of, for example, volts is derived from the supply voltage by means of a transformer 14 between the points A and B. During each period, via a rectifier 3, said alternating voltage charge charges a capacitor 4 or, for example, Znf, which is discharged during the remaining part of the same period via a resistor 5 of, for example, 15 K ohms. This is shown by the topmost diagram of FIG. 2. The time constant of the RC-network 4, 5, with respect to one period of the alternating voltage, is chosen to be sufiiciently high so that the discharge curve is substantially linear. The voltage V across the capacitor 4 between the points A and C is therefore substantially a sawtooth voltage, superimposed on a negative, rectified voltage. This voltage is superimposed on a variable bias voltage applied between the point A and the cathode of the tube 1 (point E), consisting of a fixed negative voltage of, for example, 28 volts of a first source 6 and of a variable part derived via a branch of a potentiometer 8 of, for example, 10 K ohms from the positive voltage of a second source 7 of, for example, volts. Finally, the total voltage between the points C and E is applied, via two series resistors '9 and 10 of 10 and 22 K ohms respectively, between the cathode and the control-electrode of the tube 1. This mode of varying the phase of the instant of ignition relative to the alternating voltage applied to the transformer 14 is already known from said United States patents.

The anode of the tube 1 is supplied from a directvoltage source 11 of, for example, 150 volts which charges, via a resistor 12 of for example, 6 K ohms a capacitor 13 of the eg 1 ,uf. When the tube 1 ignites, said capacitor is discharged via the primary winding of an out- 6 put transformer 15 and the anode-cathode path of the tube 1 connected in series therewith.

The second line of FIG. 2 illustrates the control of the instant of ignition. It is assumed in this case that with an alternating voltage V having a peak value of 160 volts, the discharge of the capacitor 4 extends from t to t or over a period which is equal to approximately 300 of the alternating voltage, V so that the amplitude of the sawtooth pulses amounts to about 80 volts. It is furthermore supposed that the tube 1, for example, of the type PL 5557, ignites at an anode voltage V of about +125 volts and a grid voltage of about 2 volts and has an arc voltage between the anode and the cathode of 12 volts. If the voltage between the points A and E is equal to +85 volts, the peak of the sawtooth lies at +5 Volts relative to point B (horizontal time axis passing through 0') and the tube 1 ignites at the instant t with a very long delay, about 180 after the beginning of the corresponding period of the alternating voltage. If the voltage V is equal to +148 volts, the valley of the sawtooth lies at -12 volts relative to point B (horizontal time axis passing through 0") and the tube 1 ignites at the instant I with a considerable advancement, about 60 prior to the beginning of the corresponding period of the alternating voltage.

In both cases the voltage V increases initially further subsequent to the ignition of the tube 1. 'In the first case said voltage abruptly decreases thereafter at time r and becomes negative before the discharge of the capacitor 13 across the tube 1 has terminated. The path between the control-electrode and the cathode of the tube 1 is therefore rapidly deionised by the negative voltage between the control-electrode and the cathode and the tube 1 extinguishes reliably at the instant when the voltage of the capacitor 13 drops below the arc voltage.

In the second case the voltage V increases further after the ignition of the tube 1 for about one and a half halfperiods of the alternating voltage V and is highly positive at the instant I when the tube 1 must extinguish. At this instant the path between the conrolelectrode and the cathode of the tube 1 is not deionised and the tube continues to conduct. At this time its anode current is limited by the resistor 12 to a value of The capacitor 13 cannot be charged again until the tube 1 has extinguished, which can occur shortly before or after the instant t when the voltage V has again become negative and reaches its minimum value. At the next-following instant of ignition t the voltage across the capacitor 13 has increased only little, for example, to about 45 volts and the tube 1 will not ignite until its control-electrode has become positive again. The net result is that the desired advance of the ignition of the tube 1 cannot be attained and that weak, long output current pulses will be obtained over a considerable part of the control-range instead of obtaining stronger, shorter pulses. Another possible adverse effect of the long control voltage pulse V on the circuit is that the eratic firing of tube 1 caused by premature ignition thereof. For example, in the case where tube 1 is ignited at time t the discharge of the anode capacitor 13, shown in dashed lines in the last diagram of FIG. 2, is completed at time r at which time tube 1 is extinguished. From this instant on capacitor 13 begins to charge again. However, the voltage V is still rising positively, and at some instant before time 21 the capacitor voltage may rise to a value sulficient to ignite tube 1, since its control electrode is at a high positive voltage too. As a result, tube 1 ignites prior to time 1 producing a weak output pulse at the wrong point of the cycle. At the next following instant of time t capacitor 13 may or may not have reached a sufiicient voltage to ignite tube 1, but even if it does ignite, the

output pulse produced will be weak since there was insufficient time to fully charge the capacitor.

In order to overcome these difiiculties and to be able to produce, throughout the phase control-range, strong output pulses with an accurately defined leading edge and trailing edge, a second gas or vapor-filled discharge tube 2 is employed, in accordance with the invention, the main current circuit of which is connected, via the resistor 10 and the source 6 of negative bias voltage, in parallel with the path between the control-electrode and the cathode of the tube 1.

As is shown, the tube is a gas-filled tetrode, e.g., of the type PL 2 D 21. Its cathode is connected to the common point D of the source 6 of negative bias voltage and of the variable part of the source 7 (tapping of the potentiometer 8) and its anode is connected to the common point of the resistors 9 and 10. The first grid of the control-electrode of the tube 2 is connected to the tapping of a potentiometer formed by resistors 16 and 1-7 of and 200 K ohms respectively, said potentiometer being connected in parallel with the cathode-anode path of the tube 2. The second grid of tube 2 is connected via a resistor 18 of, e.g. 10K ohms to the cathode. Thus the control-electrode of the tube 2 becomes positive at the same time as the anode and the tube thus ignites even at a low anodecathode voltage V of, e.-g., 32 volts at the instant t and t respectively, shortly after the ignition of the tube 1. Its arc voltage amounts to not more than 8 volts, but owing to the voltage drop across the resistor 9 the tube extinguishes at a voltage V of about 20 volts, which corresponds to a voltage V of 8 volts.

At the instant t or t respectively, shortly after the ignition of the tube 1, the control-voltage V applied to this tube abruptly decreases and becomes immediately negative due to the discharge of the tube 2. This voltage remains negative, e.g., equal to 20 volts, until the sawtooth voltage has decreased to an extent such that the tube 2 extinguishes and from this instant it becomes still further negative with the voltage V Since shortly after the ignition of the tube 1 a negative voltage of at least 20 volts is applied between the control-electrode and the cathode, this tube is rapidly deionised subsequent to the discharge of the capacitor 13 via the anode-cathode path. In this way, tube 1 extinguishes with certainty in spite of the fact that the control-voltage V increases further or tends to increase further. The resistor 10 serves to limit any ion flow passing through the negative control-electrode of the tube 1.

Owing to the use of the auxiliary tube 2, output pulses of constant width and amplitude can be produced, as is illustrated by the third line of FIG. 2, independent of the phase of these pulses relative to the alternating voltage V which is variable over a range of more than 240.

The circuit arrangement according to the invention may also be employed when the anode of the main tube is energized in a manner differing from that shown in FIG. 1, for example, if it is energized by a sinusoidal or nonsinusoidal alternating voltage, superimposed or not superimposed on a direct voltage. However, this voltage must become lower or tend to become lower than the arc voltage of the main tube at least once per period of the sawtooth control-voltage.

What is claimed is:

1. An electric circuit comprising a first gas or vapor electric discharge tube having an anode, cathode and control electrode, an output circuit connected to said anode comprising means for applying thereto a varying voltage, means for producing a discontinuous control voltage having 'a progressively varying leading edge, a control circuit connected to said control electrode and including input means for applying said control voltage to said control electrode to control the ignition of said tube, said control circuit further comprising a resistor, a source of direct bias voltage, a second electric discharge tube having an anode and cathode which define a current path therein, and means for connecting said resistor, said second tube and said bias voltage source in series circuit across said control electrode and cathode of the first tube with said bias voltage source connected in the reverse bias sense, and means for applying said control voltage across the current path of said second tube so as to ignite said second tube a given period of time after said first tube is ignited thereby to connect said bias voltage source to said first tube control electrode via said second tube current path and said resistor in said reverse bias sense to extinguish any discharge between said first tube cathode and control electrode.

2. A circuit as described in claim 1 further comprising a second resistor serially connected between said control voltage producing means and the current path of said second tube.

3. A circuit as described in claim 2 wherein said second tube has a control electrode for initiating conduction in said tube current path, said circuit further comprising a voltage divider connected in parallel with said second tube current path, and means connecting said second tube control electrode to a tap on said voltage divider.

4. A circuit as described in claim 1 wherein said output circuit voltage applying means comprises means for .pro ducing a varying direct voltage which periodically attains an amplitude equal to the tube arc voltage.

5. A circuit as described in claim 4 further comprising a second source of variable direct bias voltage serially connected with said control voltage producing means across said control circuit input means thereby to adjust the ignition point of said first tube.

6. A circuit as described in claim 1 wherein said voltage producing means is arranged to produce a control voltage having a positive going sawtooth shaped waveform.

7. An electric circuit comprising a first gas or vapor electric discharge tube having an anode, cathode and control electrode, an output circuit connected to said anode comprising means for applying thereto a varying voltage, means for producing control voltage pulses having a progressively rising leading edge, a source of bias voltage having its positive terminal connected to said first tube cathode, means for superimposing said control voltage on said bias voltage, means for applying said superimposed control voltage to said control electrode to control the ignition of said tube, a resistor, a second electric discharge tube having an anode and cathode which define a main current path in said tube, means connecting said resistor in series with said second tube current path between said control electrode and the negative terminal of the bias voltage source, and means for applying said control voltage pulses across the main current path of said second tube so that said second tube ignites after said first tube, whereby the negative voltage of the bias voltage source is applied to the control electrode of said first tube via a path comprising a second tube and the resistor to extinguish any discharge between the cathode and control electrode of said first tube.

8. A circuit as described in claim 7 further comprising a second resistor connected in series between said pulse applying means and the main current path of said second tube.

9. A circuit as described in claim 8 wherein said second tube further comprises a control electrode, a voltage divider connected in parallel with the main current path of said second tube, and means connecting the control electrode of said second tube to a tap on said voltage divider.

10. A circuit as described in claim 8 wherein said second tube is a gas or vapor filled discharge tube having its anode connected to the junction between said first and second resistors and its cathode connected to the negative terminal of said bias voltage source.

11. An electric circuit comprising a first gas or vapor electric dicharge tube having an anode, cathode .and control elect-rode, an output circuit connected to said anode comprising means for applying thereto a varying voltage, a source of direct bias voltage having its positive terminal connected to said first tube cathode, a second electric discharge tube having an anode and a cathode, means connecting said second tube cathode to the negative terminal of said bias voltage source, a resistor connected between said second tube anode and said first tube control electrode, a source of control voltage having a linearly varying leading edge, means connecting the positive terminal of said control voltage source to the junction oi said second tube cathode and said negative terminal oi the bias voltage source, and means connecting the negative terminal of said control voltage source to the junction of said second tube anode and said resistor thereby to successively ignite said first tube and said second tube, in that order, the ignition of said second tube effectively suppressing the remaining portion of the leading edge of said control voltage from afiecting the control electrode of said first tube.

References Cited UNITED STATES PATENTS 2,490,562 12/1949 Van Dorsten 315240 FOREIGN PATENTS 1,105,073, 4/1961 Germany.

JAMES W. LAWRENCE, Primary Examiner.

P. C. DEMEO, Assistant Examiner. 

1. AN ELECTRIC CIRCUIT COMPRISING A FIRST GAS OR VAPOR ELECTRIC DISCHARGE TUBE HAVING AN ANODE, CATHODE AND CONTROL ELECTRODE, AN OUTPUT CIRCUIT CONNECTED TO SAID ANODE COMPRISING MEANS FOR APPLYING THERETO A VARYING VOLTALGE, MEANS FOR PRODUCING A DISCONTINUOUS CONTROL VOLTAGE HAVING A PROGRESSIVELY VARYING LEADING EDGE, A CONTROL CIRCUIT CONNECTED TO SAID CONTROL ELECTRODE AND INCLUDING INPUT MEANS FOR APPLYING SAID CONTROL VOLTAGE TO SAID CONTROL ELECTRODE TO CONTROL THE IGNITION OF SAID TUBE, SAID CONTROL CIRCUIT FURTHER COMPRISING A RESISTOR, A SOURCE OF DIRECT BIAS VOLTAGE, A SECOND ELECTRIC DISCHARGE TUBE HAVING AN ANODE AND CATHODE WHICH DEFINE A CURRENT PATH THEREIN, AND MEANS FOR CONNECTING SAID RESISTOR, SAID SECOND TUBE AND SAID BIAS VOLTAGE SOURCE IN SERIES CIRCUIT ACROSS SAID CONTROL ELECTRODE AND CATHODE OF THE FIRST TUBE WITH SAID BIAS VOLTAGE SOURCE CONNECTED IN THE REVERSE BIAS SENSE, AND MEANS FOR APPLYING SAID CONTROL VOLTAGE ACROSS THE CURRENT PATH OF SAID SECOND TUBE SO AS TO IGNITE SAID SECOND TUBE A GIVEN PERIOD OF TIME AFTER SAID FIRST TUBE IS IGNITED THEREBY TO CONNECT SAID BIAS VOLTAGE SOURCE TO SAID FIRST TUBE CONTROL ELECTRODE VIA SAID SECOND TUBE CURRENT PATH AND SAID RESISTOR IN SAID REVERSE BIAS SENSE TO EXTINGUISH ANY DISCHARGE BETWEEN SAID FIRST TUBE CATHODE AND CONTROL ELECTRODE. 